Diabetic retinopathy is becoming the common cause of blindness in developed countries and increasing at a rapid rate. In order to better understand the pathogenesis, experimental models chiefly dogs, were investigated. However, the early stages of retinopathy could be produced in a few of these animals only after prolonged experimental period. The use of genetic selection and sucrose feeding in rats made available a model in which retinal diabetic changes could be produced within a few months in as many as 15-20 percent of the animals. During the last two years, supported by Grant RO1 EYO 1837-03 it was demonstrated in this model that castration prevents diabetic retinopathy while administration of Estradiol or Testosterone to the castrated animals increases the rate significantly. Apparently Testosterone is more effective in this respect than Estradiol. It is intended to continue and extend the study on the possible influences of a series of hormonal changes surgically or chemically produced on this experimental diabetic retinopathy. Such influences will have pathogenetic and therapeutic implications to the experimental diabetic retinopathy in rats as well as to the naturally occurring diabetic retinopathy in man. The retina will be studied in flat preparation and in histological sections by light and electron microscopy.